1. Getting started. Pull out the stems (and attached seed pods) from the chiles, tear them open and shake or scrape out the seeds, collecting them as you go.

Now, do something that will seem very odd: scoop the seeds into an ungreased medium-size (8- to 9-inch) skillet along with the torn-up tortilla, set over medium heat, turn on an exhaust fan, open a window and toast your seeds and tortilla, shaking the pan regularly, until thoroughly burned to charcoal black, about 15 minutes. (This is very important to the flavor and color of the mole.) Now, scrape them into a fine-mesh strainer and rinse for 30 seconds or so, then transfer to a blender.

Set an ungreased skillet or griddle over medium heat, lay on a piece of aluminum foil, and lay the onion slices and garlic cloves on that. Roast until soft and very dark (about 5 minutes on each side of the onion slices - peel it off the foil to turn it; about 15 minutes for the garlic - turn it frequently as it roasts). Cool the garlic a bit, peel it and combine with the onion in a large bowl.

While the onion and garlic are roasting, turn on the oven to 350 degrees (for toasting nuts), return the skillet to medium heat, measure in a scant 2 cups of the lard or oil (you'll need about 1/2-inch depth), and, when hot, begin frying the chiles a couple at a time: They'll unfurl quickly, then release their aroma and piquancy (keep that exhaust on and window open) and, after about 30 seconds, have lightened in color and be well toasted (they should be crisp when cool, but not burnt smelling). Drain them well, gather them into a large bowl, cover with hot tap water, and let rehydrate for 30 minutes, stirring regularly to ensure even soaking. Drain, reserving the soaking liquid.

While the chiles are soaking, toast the seeds and nuts. Spread the sesame seeds onto a baking sheet or ovenproof skillet, spread the pecans, peanuts and almonds onto another baking sheet or skillet, then set both into the oven. In about 12 minutes the sesame seeds will have toasted to a dark brown; the nuts will take slightly longer. Add all of them to the blender (reserving a few sesame seeds for garnish), along with 1 1/2 cups of the chicken broth and blend to as smooth a puree as you can. Transfer to a small bowl.

Without rinsing the blender, combine the green tomatoes and tomatillos with another 1/2 cup of the broth and puree. Pour into another bowl. Again, without rinsing the blender, combine the roasted onion and garlic with the toasted bread, cloves, black pepper, cinnamon, oregano, thyme, banana and 3/4 cup broth. Blend to a smooth puree and pour into a small bowl.

Finally, without rinsing the blender, scoop in half of the chiles, measure in 1/2 cup of the soaking liquid, blend to a smooth puree, then pour into another bowl. Repeat with the remaining chiles and another 1/2 cup of the soaking liquid.

2. From four purees to mole. In a very large (8- to 9-quart) pot (preferably a Dutch oven or Mexican cazuela), heat 3 tablespoons of the lard or oil (some of what you used for the chiles is fine) and set over medium-high heat. When very hot, add the tomato puree and stir and scrape (a flat-sided wooden spatula works well here) for 15 to 20 minutes until reduced, thick as tomato paste, and very dark (it'll be the color of cinnamon stick and may be sticking to the pot in places). Add the nut puree and continue the stirring and scraping until reduced, thick and dark again (this time it'll be the color of black olive paste), about 8 minutes. Then, as you guessed it, add the banana-spice puree and stir and scrape for another 7 or 8 minutes as the whole thing simmers back down to a thick mass about the same color it was before you added this one.

Add the chile puree, stir well and let reduce over medium-low heat until very thick and almost black, about 30 minutes, stirring regularly (but, thankfully, not constantly). Stir in the remaining 7 cups of broth, the chocolate and avocado leaves (if you have them), partially cover and simmer gently for about an hour, for all the flavors to come together. Season with salt and sugar (remembering that this is quite a sweet mole and that sugar helps balance the dark, toasty flavors). Remove the avocado leaves.

In batches in a loosely covered blender, puree the sauce until as smooth as possible, then pass through a medium-mesh strainer into a large bowl.

3. Finishing the dish. Return the mole to the same pot and heat it to a simmer. Nestle the leg-and-thigh quarters of the chicken into the bubbling black liquid, partially cover and time 15 minutes, then nestle in the breast quarters, partially cover and simmer for 20 to 25 minutes, until all the chicken is done.

With a slotted spoon, fish out the chicken pieces and transfer them to a large warm platter. Spoon a generous amount of the mole over and around them, sprinkle with the reserved sesame seeds and set triumphantly before your lucky guests.

Advance Preparation: The mole can be completed through Step 2 several days ahead (it gets better, in fact); cover and refrigerate. Completele Step 3 shortly before serving.